Manufacture of alkyl chlorination products



June 14, 1960 F. ROTHWEILER ETAL 2,941,014

MANUFACTURE OF ALKYL CHLORINATION PRODUCTS Filed Dec. 28, 1955 FRIEDRICH ROTHWEILER PAUL GREIF FRITZ EGGERT United States Patent MANUFACTURE OF ALKYL CHLORINATION PRODUCTS Filed Dec. 28, 1955, Ser. No. 555,987

Claims priority, application Germany Aug. 6, 1954 12 Claims. (Cl. 260-662) This invention relates to the manufacture of alkyl chlorination products of at least 2 carbon atoms.

Bios final report No. 851 discloses the chlorination of methane at elevated temperatures in a heated reaction chamber provided with internal circulation means.

This process, however, shows the disadvantage that the proportions of the resulting methane chlorination products can be varied only within very narrow limits, that the loading capacity of the reaction vessel is dependent on the heatable surface thereof and that it is not possible to go beyond a limited size of the reaction vessel as its dimensions depend upon the proportion of the heatable surface to the reaction volume.

In the case of the known reaction vessel of about 5 m? of total reaction space (reaction chamber and auxiliary reaction chamber) the relative proportions of the reaction products may be varied within very-narrow limits only, as practically only mixtures of fresh gases containing about 16% by Volume to about 20% by volume of chlorine can be treated. 7

Fresh gas mixtures of a lower chlorine content, i.e. with an increasing excess of methane, which would otherwise give an increase of the proportion of the methane chlorination products of lower chlorine content, cannot be treated in this system, as the amount of heat which is necessary in order to reach the starting temperature of more than 320 C. cannot by introduced from outside to the reaction chamber, as in such an event the high temperature of the walls would effect the thermal decomposition of the methane chlorination products.

On the other hand, fresh gas mixtures of a higher chlorine content which, according to the law of mass action, would otherwise lead to an increase of the proportion of the methane chlorination products of high chlorine content, likewise cannot be treated as the reaction heat, due to the insufiicient circulation ratio within the reaction chamber, viz. of only 2:1 to 3:1, would cause an inadmissible rise of temperature and, consequently, a thermal decomposition of the methane chlorination products accompanied by the splitting off of carbon.

In this connection circulation means that the gas in the reaction chamber is continuously thoroughly mixed by an appropriate device, for instance a conduit provided with a jet, in a similar manner to the use of a stirrer in the case of reactions occurring in solutions. Thereby, the gas already present in the reaction chamber is mixed, in a definite proportion, with fresh gas. This proportion is called the circulation ratio.

Moreover in the cited process the reaction chamber can only be charged in a restricted manner. The additionally needed amount of heat for maintaining the reaction is provided by heating the reaction chamber externally, although the reaction itself is exothermic and yields 1000 kilogram-calories of heat per m. of reacted chlorine. Of this amount of heat which, in the course of the reaction, is taken up by the total gas quantity (fresh gas and circulation gas) only 2.5/ (2.5 +l)=2.5/ 3.5 =7l.4% is transferred to the fresh gas mixture in the conduit, if the ice internal circulation ratio is,-for instance, 2.5 :1, whereas 28.6% leaves the reaction chamber in the reaction gases. When a starting temperature higher than 320 C. is to be reached behind the conduit, about 10% to about 15% of the heat set free by the reaction must be supplied to the reaction chamber by external heating. Consequently, the course of the reaction and the loading capacity of the reaction chamber are directly dependent on the heatable surface. 'If, however, an attempt is made still further to increase the loading capacity of the reaction chamber, the supply of heat through the wall of the reaction vessel must also be increased. In the case of a given area of surface of the reaction vessel this increase in the heat supply would lead to wall temperatures elevated to a degree Which would cause a thermal decomposition of the chloromethanes formed, accompanied by the splitting off of carbon. 7

As the ratio of the surface of the reaction chamber to its volume diminishes with increasing size of the reaction chamber, the possibility of enlarging the reaction chamber is limited.

All the difiiculties mentioned above for the chlorination of methane also arise if hydrocarbons of 2 or more carbon atoms are to be chlorinated in said reaction chamber.

This application is in part a continuation of application Ser. No. 525,862, filed August 2, 1955, now abandoned.

In the copending application Ser. No. 441,874, filed July 7, 1954, now abandoned, for Process for the Mannfacture of Methane Chlorination Products, it is described to prepare methane chlorination products by reacting in an adiabatic manner mixtures of chlorine with methane or with methyl chloride, methylene chloride or chloroform or with mixtures thereof, if desired in the presence of an inert gas, at an elevated temperature below the decomposition temperature of the methane chlorination products. By adiabaticreaction? is meant that during the exothermic reaction no heat' is supplied to the reaction gases by heating or withdrawn therefrom by cooling.

Now, we have found that alkyl chlorination products which contain atllea st two carbon atoms can be prepared by reacting mixtures of chlorine with saturated aliphatic hydrocarbons or with chlorinated aliphatic hydrocarbons containing at least 2 carbon atoms, such as ethane, ethyl chloride, ethylene chloride or mixtures thereof, propane or chlorinated propanes, n-butane, iso-butane, mixtures of nand/or iso-butanes and chlorinated butanes, monounsaturated hydrocarbons such as ethylene, propylene or butylenes, or vinyl chloride, vinylidene chloride etc., if desired in the presence of an inert gas, at a temperature above the starting temperature and below the decomposition temperature of the alkyl chlorination products and generally in the absence of catalysts, in a reaction chamher which allows of carrying out the chlorination-which is an exothermic reaction-without any substantial transfer of heat through the walls of the reaction chamber. This means that the reacting gases are neither cooled nor heated from outside during the reaction. The reaction according to the present invention, therefore, requires a well heat-insulated reaction chamber. Any heat losses which are still caused by radiation are of no importance in comparison with the heat quantities present in the reaction chamber. The use of catalysts, though possible, does not offer any advantages.

The process of this invention compared with the known one, offers the following advantages:

The relative proportions of the aliphatic hydrocarbon chlorination products formed can be varied within wide limits and the loading capacity of the reaction chamber is independent of its surface. Furthermore, the reaction chamber can be enlarged to any desired extent as, ac-

' reaction chamber.

'ucts are determined by 'the law of mass action. Fresh gas mixtures with a substantial excess of the starting material, for instance ethane, as compared with chlorine,

ing materials as are liquid at room temperature'are, from "the beginning, either heated to temperatures above the 7 chlorine may in this casel'ikeviiseibe introduced at a tempreferably yield a mixture of'hydroarbons..the major,

part of which is a chlorinated hydrocarbon containing ,1

. chlorine atom more than the starting product, ,inthis example ethyl chloride, with a reduced excess of starting material whereasrfresh gas mixtures form large amounts of the higher chlorinated ethane chlorination products. By adding higher chloro-alkanes, e.g. chloro-ethanes and/ or an inert gas-singly or together-40 the fresh gas mixture, the relative proportions of the chlorination products formed can also be varied according to the law of mass action. Q

When a definite number of chlorine atoms is to .be introduced into the molecule, it 'is of advantage'to cool thegas mixture containing -the chlorination products,

which have primarily been formed, tofsuch a degree that.

the portions which arernore difiicultly' volatile are condensed and then to reintroduce the non-condensed products into the reaction chamber. The better the conden- V {sable products, for example alkyl monochlorides, are

separated from the gas mixture obtained during the reaction, the more homogeneous is the reaction product.

In view of the specific performance of the reaction it is. furthermore possible to render its course independent of .the heating of the reaction chamber. This result is attained by increasing the'ratio of the internal circu lation' (proportion of circulating gas to fresh'gas entering) higher than 3:1 and by selecting an appropriate inlet temperature of the fresh gas mixture. By dispensing "with heating of the reaction chamber its loading capacity becomes independent of its surface. V

f Irrespective of the amounts of gases fedto the reaction chamber, the above measures allow of'rnaintaining, during the reaction, temperatures exceeding the starting temperature of the reaction, ie higher than about' 2 5l) to about 320 C., and remaining below'thedecomposition temperatures of the alkyljchlorination products, i.e. below about 420 C5500" C; The course'of the reaction within the range of these temperatures is guaranteed.

It is to be noted that the starting temperature is different a for each substance and is, in general, between about 250 C. and 320 C. V

A. formation of carbon caused by the thermal decomposition of the reaction products cannot take place as even local superheating is completely excluded by dispensing With the external heating of the reaction chamber and 7 by the large internal circulation ratio.

By increasing the internal circulation ratio, e.g. to 5:1, the process of the present invention permits of trans ferring to the fresh gas 5/(5+1)=5/6 =83.3% of the amount of heat liberated by the reaction, whereas only 16.7% leaves the'reaction chamber in the reaction gases. In this manner it is possible in the conduit to exceed the starting temperature Without additional external heating of the reaction chambeniif, forinstance, a fresh gas mixture containing 16% by volume to 17% by volume of chlorine is introduced into the reaction chamber at room temperature, by which term, here and below, a temperature of about 20 C. is to be understood. The fresh gas mixtures of gaseous alltyl hydrocarbons containing a higher percentage of chlorine advantageously have aninlettemperature below room temperature down to about -20 C. and those of a lower percentage of chlorine advantageously have an inlet temperature above room temperature. The fresh gas mixtures of such. startperature below the boiling point of said starting',materials and diluted 'byan inert gas.' The freshga S'mixjtures .are .then' circulated in the "usual, manner :together with the reacted .gas which: has a temperature corresponding to the temperature of reaction. a

The present process can be carried out as follows, using an apparatus as illustrated diagrammatically in the accompanyingdrawing z; i Q H Referring to the drawing, an aliphatic hydrocarbon or chlorinated hydrocarbonbr' mixtures thereof to which also aninert gas may be added is passed into a preheater 1, and from there to a heat exchanger 2. a 'In a mixing device 3 chlorine is added to the organic starting material, ,and this fresh gas mixture is passed to the reaction chamber 4. j V V a By means of a circulation device, consisting for instanceof ajet 5 and a conduit 6,'reacted gas is taken in at the temperature of reaction and mixed infthe'con- 'duit with the fresh gas mixture in afproportion higher than 3 1. By means of the reacted gases drawn from the reaction chamber into the circulation device at a reaction temperaturejor 'about' 300" CL to'about 420 C.,

fthe' fresh gas mixture, mixe'dtherewitli in the conduit, is

heated to. atemperature higher than the starting temperature. The'heatset free during the reaction j'then raises the temperature of the mixed gas to the final temperatu're of the reaction amountingjto about 300 C; to about T C. The reaction of the chlorine is nearly complete. The residual chlorine is, if desired, jfinally reacted in anauxiliary reaction chamber 7, only an'insignificant proportion thereof beingleftunreacted, so that the mixture of the final reaction gases. contains less than 0.05% vby volume ofchlorino.

In theheat exchanger lithe" gaseous mixture can transferitsheat to the'starting mixture. The preheating need .not be restricted to the organic starting material. If

desired, all the reactantsgincluding the chlorine as' such or in admixture, can be preheated to any temperature below the starting'ftemperature of the reaction; The 'said'reaction' can, however, also be carried out without preheating of the reaction gases or the'mixtures of reaction gasees. Of course, it is alsopossible toeifect a preheating only in preheater *1 or only in heat exchanger 2.

For economic reasons it is advantageous to use the heat of the gases leaving the reactioncharnber for'preheating. 7

The above described circulation device consists of a jet and a conduit. Its elficiency can be improved by making use of experience gathered in applied aerodynamics.

The circulation can 'also be efiected by other means ap-' plied in industrial practice V V a In the above described system the circulation device consists of .a cylindrical jet and a cylindrical conduit. The dimensions are, indicated in the following tabulation.

EMBODIMENT I Reaction chamber including auxiliary Internal diameter 1200 mm.

7 7 cross section of jet 1' V 10( Rate of supply of fresh gas mixture-.. 200 milhr. to 1200 mfi/hr. at

a 1 Circulation ratio measured in a blank test Higher than 3 to about 7. r

by means of air.

With a conduit or an internal diameter of 400 mm. and a length of 3000 mm., a ratio F f=about 37 is preferably EMBODIMENT II Reaction chamber including auxiliary Internal diameter 1800 mm.,

reaction chamber. length 9000 mm. Total capacity 23 m3 .Tet Internal diameter 160 mm.-

Cnndnit 80 mm. Ingelrnal diameter 850 mm.- cross section of conduit F R atio cross section of t Higher than 25 up to about Rate of supply of fresh gas mixture.- wait /hr. to 4000 Circulation ratio measured in a blank test Higher than 3 to about 7.

by means of air.

With a conduit of an internal diameter of800 mm. and a length of 6000 mm., a ratio F/) of about 45 is preferably chosen, the resulting ratio of the internal circulation being about 5 and the total quantity of fresh gas fed to the reaction chamber amounting to between about 600 m. /hr. and about 4000 m. /hr. measured in a blank test by means of air. The total quantity of fresh gas of 4000 m. /hr. can, however, be exceeded by about 50%.

The above mentioned figures apply for a slightexcess pressure in the reaction chamber amounting from about 1 to about 2 atmospheres (absolute) and for a pressure drop from a few cm. of water to a few or. of water in the jet. If the pressure conditions change, these figures have to be altered. In the indicated quantity ranges the internal circulation ratio is practically constant in the case of the given dimensions. V v i When designing the circulation device it must betaken into consideration that the effective concentration of chlorine in the reaction chamber diminishes with increasing circulation ratio.

The dimensions of reaction chambers of a smaller or a larger volume than exemplified in Embodiments I and II can be derived from the figures given for the two embodiments. i t

The method of-mixing the fresh gas with the circulation gas in the reaction chamber can in practice he changed by additional installations. Such additional devicescan be installed, for instance, in the conduit, in the annular section formedby the conduit and the reaction chamber and also in the lower and the upper parts of the reaction chamber. It may also be advantageous temporarily to heat the reaction chamber externally, for instancewhen starting and in order to avoid heat losses caused by radiation during interruptions of operation, i.e. to provide for the heat capacity of the reaction vessel itself.

As described above, the reaction chamber can be followed by an auxiliary reaction chamber 7 in which the residual chlorine can be reacted. This auxiliary reaction chamber can be heated and/ or be provided with heatretaining substances which should advantageously be nonporous, for instance flint and porcelain, or with catalytically active filling material. It can be installed inside or outside the main reaction chamber As constructional material for all parts of the reaction chamber, the auxiliary reaction chamber and other parts of the installation which come into contact with the reaction gases, nickel or nickel-containing steels are advantageously used.

As can be seen from the examples below it is' possible in the course of the reactions according to the present invention to change, within wide limits, the relative proportions of the reaction products formed by varying the conditions of reaction. This is achieved by selecting an appropriate inlet temperature of the fresh gases, by altering the composition of the fresh gases, particularly as regards their chlorine content and by maintaining a suitable internal circulation ratio.

.The following examples illustrateihe invention and relate to operations: carried out by means. of a continuously working circulation apparatus with a reaction chamber :accordingto Embodirnentl. Forstarting the reaction, the reaction chamberis heated-up the the starting temperature.- can, for instance, be effected by heating the reaction chamber externally and by causing hot circulation gas to flow through its interior. When the starting temperature is-reached, thereaction' is started by adding chlorine to the circulation gas containing at least one of theorganic materials described above. As soon as the desired temperature inthe reaction chamber is reached, the reaction is conducted continuously under the conditions described in the examples.

The following examples serve to illustrate. the invention but they are not intended to limit it thereto; the relation between units of weight and units of volume is the same as thatbetween the kilogram and the liter.

Example 1 A mixture of 27% by volume of chlorine and 73% by volume of ethane is reacted at 390 C. The inlet temperature of the fresh gas entering thereaction chamber is i y The chlorination products formed consist of 87 .2% by weight of ethyl chloride and 12.8% by weight of dichlorethanes. The/conversion is, as in the following examples, almost complete. Consequently, less than 0.05% of chlorine are contained in the reacted gas mixture.

Exar nple v '2 e In order to-obtain a higher yield of dichlorethanes, the condensation of the chlorination products primarily formed at 390 C. according to Example lis carried out at +16 C. and'the products'which have not been condensed during this process, i.e. chiefly the ethyl chloride, are returned as recycle gas to the reaction chamber where they are reacted once more with-chlorine. Fresh ethane is added only pari passu with its consumption. Before the reaction the gas mixture contains; 16.5% by volume of chlorine, the rest is recycle gas. The inlet temperature of the fresh gas is about +25 C. 4

The mixture of the chlorination products formed contains':

f f Percent by weight Ethyl chloride H 18.4 1.1-dic'hlorethane 37.2 1.2-dichlorethane 32.6 Higher chlorinated products, 11.8

v I i Percent by weight Isopropylchloride 18.2

n-Propyl chloride 34.6

1.2-dichlorpropane -i 43.2

1.2.3-trichloropropane 4.0

' Example 4 mixture of 33% by volume of chlorine and 67% by volume of technically pure butane is reacted at 275 -C'. "The butane isintroduced. into the reaction chamber The chlorination products formed consist of 49% by weight of 2-chlorobutane, 24% by weight of 1- chlorobutane, 22% by weight of 2,3-dichlorobutane and 5% byweight of 1,2,3-trichlorobutane.

Example 5 'A mixture of 60% by volume of ethylene, containing about 4% by volume-of ethane, and 40% by volume of a I-Iigher boiling mixture:ofachlprrnatedg-cthanes and time of nomreaeted chlorinek 1 a gas isabout +60Q C The leaving as .aa uagenaas j a me a rsal;-

reacted' chlorine. Under splitting off of HCI, 15,596

chlorine islrated at 1345 C Theihiet temperat ure er the "fresh gas is; about- *2; lowboifing wmyl i gestion gas a';

Vinyl ..cnoaaa';

I ethylene 11.9

a U 5 Exa p es V l V. A mixture of 7 5% by-volume -sof iteclinicallypurevinyl chloride and 25% by =volume of chlorine is reacted at about +2 0. V j r F1 1 lc astisei dmV e t -95 a i Percent by'weight Mixture of, v1; l-dichlorethylene and r1'.2-dichlorethylene I p f 1 "45.0 Higher boiling V ture of -.chlorinated ethanes and methylenes' 5 I V g 55:0

1-; f 3' 51:1; A mixture of 75% "woluihe of technically pure '30 ethyl chloride and 25% by-yolume ofchlorine -.is creacted at l ih uin etper m e the-fresh +39 0 C. The inlet temperature of the fresh gas is 20 The chlorination;prbducts'forxnedlcensist u r a ippelr-cntiby'wighf Vinyl chloride mix i h bn ing- 'mixmre er chlorinated charms and a by volume of the ethyl chloride used are transformed into i' i i l i ii ur shl i ated erh ne and a 69 rthilhss .7 r a r 511.7

The leaving gas mixturegoontains up to 0.2% by volume of chlorine. Under splitting off-0ft HCl, 20% by volume of the'cthyl chloride ius'ed a re' tralnsf orme d into ethylene and j'dbtained 'a's 'suchil The amount er ncl split off during this procedu'r'is thereupon to be fonnd in the wastegas. it v I JWe claim:.. 1p r 5 '1. In a process for the continuouslpreparation -of alkyl 70 chlorination products-by reacting chlorine a com pound selected from the group consisting of aliphatic hydrocarbons containingZto 4-=carbon atoms and at most one double bond; :the correspondiag chlorinated -c0mpounds and thereof at 1temperaturesibetweett mar na a a a about the starting temperatures of the reaction and about SOO C. without-any*substantial transfer ofheat t'hrough 'the w ns 6ft-he reacaen-ehamber, t e 'steps=which com'- prisecent'rolling the reaction temperature bycirculating the majonpoi'tion of the reactefd gases 'withiri the'reaction chamber siibstantially parallel to theyvallspf said react-ion chamber and by" mingling less than bnepart 5y volume of the gas mixture o'f the starting nraterials'with 3 parts by volumet'offthe circulatinggreacted gases which are at reaction temperature. a r V 2. A process according to claim 1 wherein-' the'gas mixture starting m i'sj siint odu ed:intoii het ea ti n r chamber at a temperature between about 20 C. and

' 3. A pro'cess according toclaim-l-wherein -.the reacted gas is mixed at the'reaction temperature with the .freshly introduce'diunreacted gases. f f

I 4. A process according to claim, 1 whereinthe reaction is carr'ied out iii-the presence of aninert'gas. T 7 5. A process 'accordingtocla'im 1 wherein at least a partof theliquid reactants is sprayed into the reaction chamber. p p 7 'f "6. A process according to claim 1 wherein ethaneis used'as startingmater'ial.

7; A process according to claim wherein ethylene das'startingmaterial; V 1 A proces'sfaccor'ding to" claim '1 wherein propane is use asst'a'rtinggmater'ialg I I 9L process according to ''claim' 1 wherein butane is usedasstafting'materia'lr o 1 l0. process for the 1 continuous, "preparation of"alkyl chlo nation products which comprises reacting chlorine was compomfdselected from the group consisting of aliphatic hydrocarbons, containing 2 to 4 carbon'atoms r and aem 'se' ae double bond, the corresponding 'chIori-r r nated cfimpbundsandmixtures vthereof 'atya temperature between abou t'250 t'o 32b C. and about 420 to 500 C. without any substantial transfer of heat through the walls ef the reaction "chamber, the reaction temperaturebeing maintained bYr'ecircuIating the major portion 'of ;-th e"reactd '-'-"gases "within the "reaction chambefisubrtahtially parallel to the walls of said reaction chamber 'tomingle 'Wit'htheum'eacted gasessupplied'to said reaction cham starting m'ater'ialsfbeing entered per 3' parts byiv'olurne of the circula'tin'g reacted gases. 7

-"11. In aiprocess-for preparing allryl chlofinationtprod whiehmo'mprises continuously reacting chlorine with a compound selected from the group consisting ermifahati'c 'lryklro'carbt'ms" containing 2 'to' 4 carbon atoms and at most one double bond, the corresponding chlorinated compounds and mixtures thereof at temperatm'e's "between about the starting temperatures of the reaction and about 500" C. withoutfanyrsubstantial transfer 'ofheat throughthe wallsyofiflie react'ion chamber, the 'step's which comprisemaintainingihe reaction temperature by circulating the major portion 'offt'he reacted gases sub- 7 stantially-parallel to. the walls 'ofthe reaction chamber and ,rriinglin'g less than one part "by fvdlume of the :gas mixture of thestarting'rnaterials "with 3 partsbyyolume of the circulating reacted gasesiwhich are at rea'ctio'n't'emperature and completing the reaction in a second v stage by conducting the reacted gases which contain small amounts ofunreacted igas through an .auxiliary reaction chamber. 12. -1n aprocess for the continuous; preparation of alkyl chlorination products by reactinglchlorine with a compound selected from the group consisting of aliphatic hydrocarbons containing two to four 'carbonsatoms and at most one double ;bond, the c'orresponding chlorinated compounds and mixtures thereof at temperatures between about the starting temperatures of the reaction and about SOOT C. without any substantial transfer of heat through the walls of the reaction chamberythe steps =which'com? prise introducing a fresh mixture of the starting mate- References Cited in the file of this patent fog!!! infbzifljet streatm, into and 1119118 Iii: lgflgi- UNITED STATES PATENTS 1n axis 0 a u ar reac 1011 zone w1 m sal c amher from an opening in the chamber remote from the tui g f g =bular reaction zone and controlling the reaction tempera- 5 2806768 g a 1957 ture by circulating the major portion of the reacted gas en er at within and substantially parallel to the walls of the re- OTHER REFERENCES mm chamber and mmglmg we Pm by the Hochst: B.I.O.S. Final Report No. 851, Item No. 22,

fresh mixture of the starting materials with at least three parts by volume of said reacted gas which is at reaction 10 temperature.

pages 1-12 and 3. 3 sheets of drawing (only first two sheets of drawing) (Figs. 1 and 2 are needed). 

1. IN A PROCESS FOR THE CONTINUOUS PREPARATION OF ALKYL CHLORINATION PRODUCTS BY REACTING CHLORINE WITH A COMPOUND SELECTED FROM THE GROUP CONSISTING OF ALIPHATIC HYDROCARBONS CONTAINING 2 TO 4 CARBON ATOMS AND AT MOST ONE DOUBLE BOND, THE CORRESPONDING CHLORINATED COMPOUNDS AND MIXTURES THEREOF AT TEMPERATURES BETWEEN ABOUT THE STARTING TEMPERATURES OF THE REACTION AND ABOUT 500*C. WITHOUT ANY SUBSTANTIAL TRANSFER OF HEAT THROUGH THE WALLS OF THE REACTION CHAMBER, THE STEPS WHICH COMPRISE CONTROLLING THE REACTION TEMPERATURE BY CIRCULATING THE MAJOR PORTION OF THE REACTED GASES WITHIN THE REACTION CHAMBER SUBSTANTIALLY PARALLEL TO THE WALLS OF SAID REACTION CHAMBER AND BY MINGLING LESS THAN ONE PART BY VOLUME OF THE GAS MIXTURE OF THE STARTING MATERIALS WITH 3 PARTS BY VOLUME OF THE CIRCULATING REACTED GASES WHICH ARE AT REACTION TEMPERATURE. 